Saying that he had a change of heart on the third day of a trial that has shocked the world, he said: “I declare myself guilty of the charges in the indictment.”

In a statement to the panel of judges, Fritzl (73) referred at one point to what he called “my sick behaviour”.

He told the judges his daughter’s videotaped testimony yesterday had made him change his mind and plead guilty to all charges.

Fritzl expressed regret that he did not bring the ailing infant out of the dungeon and get medical help.

“I don’t know why I didn’t help,” he said.

“I just overlooked it. I thought the little one would survive.”

Asked by the presiding judge what had led him to change his mind, Fritzl said it was the testimony from his daughter that he, jurors and the rest of the court had viewed during a closed-door session yesterday.

Fritzl faces life imprisonment on the homicide count, which he had initially denied along with an enslavement charge.

He was also charged with rape, forced imprisonment and coercion.

Wearing a mismatched suit and a blue shirt, Fritzl did not hide his face behind a binder as he had done for the last two days when led into the courtroom in St Poelten, west of Vienna, today.

His daughter Elisabeth was the key witness. Now 42, she was 18 when he imprisoned her in the cramped, windowless cell he built beneath the family’s home in the town of Amstetten.

Fritzl had been charged with homicide over the death of an infant — a male twin born to Elisabeth in 1996 — who might have survived with proper medical care.